1. Field of the Invention
This invention relates to a cooling arrangement for direct injected engines and more particularly to an improved cooling arrangement for fuel injectors that spray fuel directly into combustion chambers.
2. Description of Related Art
As is well known, in all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. This trend has resulted in the substitution of fuel injection systems for carburetors as the engine charge former. In the common systems used, fuel is injected into an intake air manifold. In order to obtain still further improvement, direct injection systems are being considered. These systems inject fuel directly into the combustion chamber and thus have significant potential advantages.
With direct injection systems, however, since the fuel must be injected directly into the combustion chamber, a nozzle of the fuel injector is exposed to the combustion chamber in which the injected fuel burns at an extremely high temperature. Although cooled with the injected fuel per se before every combustion, the injector nozzle retains considerable heat therein with the repeated combustions.
It is, therefore, a principal object of this invention to provide a cooling arrangement that is allowed to keep an injector nozzle under the evaporation temperature so as to ensure correct controls and improve emission control.
The aforenoted problems are likely to occur particularly in conjunction with engines in which a plurality of cylinder bodies extend vertically. In those engines, cooling water flows generally upwardly and downwardly and backwaters or pools can be formed in the water flow due to the gravity. Outboard motors usually accommodate such engines.
It is, therefore, another object of this invention to provide an improved cooling arrangement that is applicable to this kind of engines.
Meanwhile, a certain amount, although it is small, of the liquid fuel that contains heavy oil components exists on the injector nozzle immediately after injection. When the heat in the injector nozzle exceeds the evaporation temperature of the liquid fuel (for example, 90% of gasoline components evaporate at 150.degree. C. to 170.degree. C.), the heavy oil components tend to deposit on the injector nozzle. Excessive depositions of the heavy oil components on the injector nozzle invite deformations, of the injection shape and fluctuations in the amounts of injected fuel and then give rise to incorrect controls and difficulties in control of emissions. The injector nozzle exposed to the combustion flame reaches the evaporation temperature without delay after startup of the engine.
Notwithstanding the improved cooling arrangements, it is more effective to ensure correct controls and easiness in control of emissions in case that heavy oil components in the liquid fuel deposit on the injector nozzle due to some reasons. For example, the cooling water may be precluded from flowing smoothly due to an impermanent malfunction of a water pump.
It is, therefore, a further object of this invention to provide an improved control system that can adjust amounts of the fuel so that the appropriate fuel amount that match the engine's requirement is injected at every injection.
In this regard, it is found out that the drop rate of injection amounts decreases with a lapse of time and then settles a constant value. How the injection amounts decrease and the constant value depend on the temperature of the injector nozzle. Accordingly, it is one idea to use a temperature sensor and the relationship of time versus temperature to control the injection amount. However, the temperature sensor is somewhat costly. In addition, it requires to be attached to the injector nozzle per se. This can cause, however, another problem in securing the attachment because the fuel injector is detachable.
It is, therefore, a still further object of this invention to provide another improved control system that is not costly and requires no complicated arrangement.